Retinal function is dependent upon the excitation of photoreceptor membranes. Although calcium is involved in controlling membrane conductance and is therefore essential to photoreceptor function, the site of CA2 ion storage and mechanisms of transport from the blood vessels to the retina is not yet completely known. Therefore it is the objective of this proposed investigation to establish the content and distribution of both soluble (diffusible) and bound Ca2 ion in the cells of the retina and choroid in normal (light and dark-adapted) eyes. Preliminary studies suggest that the retina pigment epithelium and its associated pigment granules play a significant role in the storage and maintenance of Ca2 ion for the retina. Therefore these pigment granules, as well as the pigment found in the choroid, ciliary body tapetum, iris and rod outer segments will also be analyzed for the presence of Ca2 ion (in light and dark adapted eyes). Identical tissue preparations from albino eyes (amelanotic) will be analyzed for comparison. Analyses will be made by atomic absorption spectrophotometry, thin section and bulk x-ray microanalysis and ultrasoft x-ray contact microscopy of unfixed quench frozen (sectioned and bulk) tissues as well as conventionally prepared freeze-dried and plastic embedded cells. The content and intracellular compartmentalization of Ca2 ion (and equally essential cations) in normal ocular tissues will also be compared to tissue removed from young and mature animals with retinal degeneration resulting from diabetes and retinitis pigmentosa in order to establish if there are any alterations in the Ca2 ion or cation deposition which precede retinal degeneration and the eventual loss of vision.